P0721: Output speed sensor: range/performance
The gearbox output speed does not match wheel or engine speed; usually a dirty sensor, a poor contact or electrical interference.
| Code | P0721 |
|---|---|
| System | Engine and transmission |
| Group | P07xx, Transmission |
| Type | Generic: it means the same on every make |
| Can you keep driving? | With care |
What P0721 means
The output speed sensor measures how fast the shaft leaving the gearbox towards the wheels is turning. The control unit uses it to decide when to shift and, on many cars, it also feeds the speedometer or other systems. This code means the signal arrives but is not consistent: it jumps, drops out at times or does not fit the speed measured by other sensors, such as the ABS ones.
Most common causes
- Sensor covered in metal particles or not fitted securely
- Loose or corroded connector
- Damaged or poorly shielded wire picking up interference
- Tyres of a different size from the original
- Faulty sensor
- Transmission control unit fault (uncommon)
Symptoms
- Speedometer failing, flickering or dropping to zero
- Harsh or oddly timed shifts
- Gearbox stuck in one gear (limp mode)
- Engine or gearbox warning light on
Can you drive with P0721?
With care You can drive with care, but the gearbox usually locks into one gear and acceleration suffers. Get it to a garage soon and avoid long trips like this.
Open the bonnetthe in-depth explanation
How to check it
Check whether the speedometer works properly: if it fails at the same time as the code appears, it points to the output sensor or its wiring. On the scanner you can compare the vehicle speed reading with a GPS.
How to read and clear P0721 with Final OBD
Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0721 with its description and whether it’s confirmed, pending or permanent.
This code is usually stored by the gearbox control unit. If the car reports it over standard OBD, you read it for nothing with FREE; to read it straight from the gearbox control unit, with its description and clearing, you need PRO.
Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before an inspection. It’s all in how to read and clear fault codes and in inspections and OBD.
Similar codes
- P071D The gearbox mode switch B has an electrical fault
- P071E The gearbox mode switch B gives a lower signal than normal
- P071F The gearbox mode switch B gives a higher signal than normal
- P0720 Output speed sensor: circuit fault
- P0722 Output speed sensor: no signal
- P0723 The output speed sensor fails now and then
- P0724 The brake switch B circuit has a high signal
- P0725 Engine speed input to gearbox: circuit fault
- P0700 Transmission control system: fault detected
- P0701 Transmission control system: range/performance
- P0702 Transmission control system: electrical fault
- P0703 Torque converter/brake switch B: circuit fault
What does code P0721 mean?
The output speed sensor measures how fast the shaft leaving the gearbox towards the wheels is turning. The control unit uses it to decide when to shift and, on many cars, it also feeds the speedometer or other systems. This code means the signal arrives but is not consistent: it jumps, drops out at times or does not fit the speed measured by other sensors, such as the ABS ones.
Can you drive with P0721?
You can drive with care, but the gearbox usually locks into one gear and acceleration suffers. Get it to a garage soon and avoid long trips like this.
How do you clear P0721?
With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0721 comes back.
Read it on your car
Final OBD reads and clears engine faults through standard OBD for free, each one explained in plain English. With PRO it also reads the faults of every control unit, each make’s own codes included, and clears them in all of them.
